the roller block def on the 2bolt caps that all depends on how much engine youre going to be running what cr,and cam and what not.I would say take your 4 bolt caps off your other motor and have them machined to fit on your vortec block,get a kit from scat for your 383.If you can 6" rods are better but dont use any less than 5.7" rods.If this is going to be a highway cruiser I'd stick lower cr like about 9.5:1 with an .043 head gasket and a smaller cam like a 270hr magnum cam,A performer intake with a 650 holley vacuum secondary,and headers you dont really need more than a 2.25" exaust pipe.I would suggest a good bowl job,backcutting the exaust valves,and having screw in studs and guides installed.
try..
383ci 9.5:1
Vortec heads
1.52 roller rockers
270HR magnum comp cam
double roller timing chain
Performer or cyclone intake
650cfm holley or Q-jet 750cfm
headers long tube
X-pipe 2.25"
50 series df flowmasters or youre prefence some like the dynomax super turbo